Actually Tony, I don't think it gives a measure of ability,all instructors techniques are off sometimes, we are all human, but if an instructor gets mad because you didn't fall, it gives a measure of their immaturity and the size of their ego. I have never found much correlation in aikido between these two. I have trained with some shihans that would definitely punish you for not falling when they were demonstrating. I, personally, won't lend my body to someone elses ego trip of how tough and skilled they are. In the staged dynamic in which most aikido is practiced (including most of what passes as aikido randori) the give and take of changing partners tends to take the edge off the risk of incurring enmity from an instructor. I don't take falls if not necessary, but, equally, bracing yourself against kotaegaeshi with your body twisted and your head 6 inches from the mat is not all that martial either.